In New England, stones were readily available from plowing fields. Foundations were needed, so Yankee engineering said, "let's use them!"
Like any foundation, stone foundations tend to leak as they age. What we are finding when we go out to homes is that there is a smear coat of mortar over the stones on the foundations and the smear coating is falling off.
The skin, or smear coat, is a combination of sand and mortar and some additive, which is made to coat the exterior of the foundation. The smear coat that was put on is falling off or when you touch it you can push the skim coat in against the stone because it is pulling away from the foundation.
It is pulling away from the stone foundation because there may not be enough additive or because the stone is so cold and the moisture is coming through so no matter what additive was added, it won't adhere. This means that the skim coat is pulling away from the stone foundation which really creates a mess.
A skim coat is not a good solution to a leaking stone foundation. First, we have to find out specifically where it is leaking from. We have to be there during a rain storm or use a garden hose to run water.
Since it is covered mostly with skim coat, it is usually leaking where the skim coat is leaking, or we have to take some of the skim coat away. We'll see if the mortar between the stones is missing or broken down. We'll then take oakum and soak it in a polymer resin material and work it between the stones, then put a specialty mortar over that.